A bounding surface model for anisotropic and structured soils under saturated and unsaturated conditions

Sedimentary soils usually have an anisotropic structure, and they are generally unsaturated, especially at shallow depths. Existing models for anisotropic and structured soils mainly focus on saturated conditions, while the unsaturation effects are not considered. In this study, a bounding surface model for anisotropic and structured soils under both saturated and unsaturated conditions is developed. The model incorporates the anisotropy and structure effects on the mechanical behaviour (e.g., the loading collapse (LC) bounding surface) and considers the structure degradation and anisotropy evolution. Furthermore, based on experimental results in the literature, the increase in water retention capacity with an increasing degree of anisotropy is incorporated by a new anisotropy and void ratio-dependent soil water retention equation. The proposed hydro-mechanical model is validated against extensive experimental data. Comparisons between experimental and calculated results show that the behaviour of anisotropic and structured soils under both saturated and unsaturated conditions can be well captured.